This invention relates generally to an apparatus for and method of producing continuous glass filaments, and in particular, to an apparatus having a bushing and a cooling apparatus positioned beneath the bushing to induce a uniform air flow between a filament forming area beneath the bushing and the cooling apparatus to cool the area. The invention is useful in the production of continuous glass filaments that may be used as reinforcement in molded resinous articles.
In the manufacture of continuous glass filaments, glass is melted in a filament forming apparatus and flows to one or more bushings. Each bushing has a number of nozzles or tips through which streams of molten glass flow. The glass streams are mechanically pulled from the nozzles by a winding apparatus to form continuous glass filaments.
The temperature of the molten glass within the bushing must be high enough to maintain the glass in a liquid state. However, if the temperature is too high, the molten glass will not cool sufficiently so as to become viscous enough to form filaments after passing through the bushing tips. Thus, the glass must be quickly cooled or quenched after it flows from the bushing tips and forms glass filaments. If the glass cools too slowly, the glass filaments will break and the filament forming process will stop.
There are numerous apparatuses for cooling the glass filament forming area beneath a filament forming machine. Conventional cooling apparatuses use air, water, or both to transfer heat from the filament forming area beneath a bushing and cool the glass filaments.
A conventional glass filament forming apparatus 5 with a heat transfer apparatus 50 is shown in FIG. 1 and is disclosed in U.S. Pat. No. 4,662,922 to Hill et al. (Hill), the disclosure of which is expressly incorporated herein by reference. Filaments 20 are drawn from a plurality of nozzles 12 of a bushing 10 and gathered into a strand 22 by a roller 42. Size is applied to coat the filaments by a size applicator 40. A reciprocating device 34 guides strand 22, which is wound around a rotating collet 32 in a winding apparatus 30 to build a cylindrical package 24. The heat transfer apparatus 50 is located beneath a bottom plate 14 of the bushing 10 to cool filament forming area 16 beneath the bushing 10.
Another conventional filament forming apparatus is shown in FIG. 2 and is disclosed in U.S. Pat. No. 4,197,103 to Ishikawa et al. (Ishikawa). The forming apparatus in Ishikawa includes a cooling system that uses both air and a cooling fluid to cool the filament forming area 16.
The cooling system includes a heat transfer apparatus 50 with a manifold 52 and cooling fins 54 that extend from the manifold 52 between rows of nozzles 12. A cooling fluid flows through a channel formed in manifold 52. Heat from the glass is transferred to the fins both radiantly and, via the ambient air surrounding the fins and glass, convectively. Heat travels to the manifold 52 from cooling fins 54 conductively and is transferred to the cooling fluid convectively.
The cooling system also includes a cooling apparatus 60 with an air manifold 66. An air source, such as a pump, supplies air to the manifold 66 from which it is introduced on one side of the bushing 10. The air travels along the nozzles 12 and fins 54. The air is introduced during the initial start-up period of a filament forming operation. After the operation stabilizes (approximately 5 to 10 seconds after start-up), the air flow is reduced or terminated.
Cooling apparatus 60 introduces air from only one side of the bushing 10. The air quickly heats up as it flows along the fins 54 and through the filament forming area 16. As a result, an insufficient amount of heat is removed from the filament forming area and the risk of bushing breaks and shut downs of the filament forming process increases. Further, the short periods of air flow are insufficient to continuously cool the filament forming area and the filaments.
Additional conventional cooling systems disclosed in Hill are shown in FIGS. 3A and 3B. The cooling system shown in FIG. 3A includes a heat transfer apparatus 50 and a cooling apparatus 60. The heat transfer apparatus 50 includes a manifold and cooling fins 54 similar to Ishikawa.
The cooling apparatus 60 includes a tube 62 with several apertures 64 along its bottom surface. Air is supplied to a channel in tube 62 and flows through the apertures 64 to the area between banks 13 of bushing nozzles 12. The air from tube 62 is cooler than the air in the filament forming area 16. The air flow entrains and induces air from the sides of the bushing 10 along the cooling fins 54 and in a generally downward direction. The induced air flow also cools filament forming area 16.
In the cooling apparatus 60 shown in FIG. 3B, a cooling fluid tube 68 supports tube 62. Tube 68 has a passage 70 through which a cooling fluid, such as water, flows. The fluid is used in conjunction with air from tube 62 to remove heat and maintain the temperature of the filament forming area 16. In Hill, the amount of heat removed from the filament forming area is limited by the volume of air flow.
Another conventional cooling apparatus is disclosed in U.S. Pat. No. 4,612,027 to Marra (Marra). Marra discloses a glass filament forming apparatus with a cooling apparatus. Cooling apparatus 80 includes a manifold 82 having a plurality of nozzles 81 as shown in FIG. 1 of Marra. Nozzles 81 are adapted to direct streams of cooling air toward the streams of molten glass and bottom plate of the bushing 10.
Another conventional cooling apparatus is disclosed in U.S. Pat. No. 4,003,731 to Thompson (Thompson). Thompson discloses a filament forming apparatus having a nozzle 10 through which air is introduced toward the bottom plate of a bushing and the glass filaments attenuated therefrom. Nozzle 10 includes a chamber 12 with apertures 18 through which air flows into skirt 14 as shown in FIG. 3 of Thompson. The air from the nozzle prevents overheating and rapidly quenches the glass streams. However, Thompson teaches that the upward movement of the air from the nozzle serves to substantially eliminate the induction of air by the downwardly moving glass streams.
A conventional apparatus for cooling a filament forming area that uses a vacuum to draw warm air out of the area is disclosed in U.S. Pat. No. 5,693,118 to Snedden et al. (Snedden). In Snedden, hollow fins similar in shape to the conventional cooling fins are mounted to a manifold through which a vacuum is applied. Each fin includes a hollow chamber and apertures along its top wall through which warm air in the filament forming area is drawn by the vacuum.
Each filament forming apparatus has an xe2x80x9coperatingxe2x80x9d condition and a xe2x80x9changingxe2x80x9d condition. In an xe2x80x9coperatingxe2x80x9d condition, continuous filaments are attenuated from a bushing at high speeds. The attenuation of the filaments induces the air surrounding the filaments in the direction that the filaments are drawn. The flow of surrounding air induces air from the perimeter of the bushing into the interior of the filament forming area to help cool the molten glass.
A xe2x80x9changingxe2x80x9d condition occurs when some or all of the filaments are not drawn at production speed and molten glass slowly flows from a bushing. During this condition, minimal air flow is induced into the filament forming area, thereby decreasing the cooling of the filament forming area and the filaments.
The filament forming apparatus must be adequately cooled during the hanging condition to permit filament attenuation to quickly restart after a disruption. The failure to quickly restart reduces the operating efficiency of the apparatus and lowers the overall throughput.
If heat is more rapidly removed from a filament forming area, the operating temperatures of the bushing and the glass in the bushing can be raised to increase throughput. There is a need for a system that removes more heat from a filament forming area than conventional cooling systems. Also, there is a need for an improved apparatus for and method of providing a uniform air flow to a filament forming area beneath a bushing.
The disclosed filament forming apparatus and cooling apparatus for and method of inducing a uniform air flow between a filament forming area beneath a bushing and the cooling apparatus offers advantages over the prior art. The filament forming apparatus includes a bushing having two laterally spaced banks or sets of nozzles from which glass filaments are attenuated. The cooling apparatus includes an air housing extending longitudinally between the banks of tips. The air housing has a top wall and two perforated side walls defining an air chamber. Each perforated side wall is oriented at an angle with respect to a vertical plane and faces in a downward sloping direction. An air source supplies air to the air housing from which it flows through the side walls and toward the banks of bushing tips in the filament forming area. Openings in the side walls control the air flow from the air housing.
The cooling apparatus also includes an air plenum coupled to each end of the air housing. The air plenums are in communication with the air source and the air flows through the plenums and into the air chamber. Turning vanes are mounted at each intersection of the air housing and an air plenum to direct air into the air chamber. The cooling apparatus also includes a plurality of fluid cooled tubes in the air housing to control the temperature in the air chamber.
A reduction in temperature of the filaments and the filament forming area permits the filament forming apparatus to produce filaments with more uniform diameters and to increase the bushing operating temperature, thereby increasing throughput. The cooling apparatus delivers a more uniform air flow to the bushing tips than conventional systems. The cooling apparatus induces air flow to the banks of bushing tips from the within the interior regions of the bushing. The cooling apparatus reduces the number of bushing breaks and process shut downs.
Alternatively, each side wall may include an opening and a screen mounted in each opening. Alternatively, the air source may be replaced with a vacuum source and warm air in the filament forming area may be drawn from the filament forming apparatus into the air chamber by the vacuum source.